1. Field of the Invention
This invention relates to valves. More particularly, it relates to pressure-compensated valves adapted for use in the subsea environment.
2. Description of the Related Art
U.S. Pat. No. 4,456,028 discloses a relief gate valve that comprises a hollow body having an inlet and an outlet, a seat ring in the outlet having a face adapted to engage a gate, a closure mounted for movement relative to the seat ring and including a carrier having a passage therethrough in which are slidably disposed a lipped gate disc adapted to engage the seat face and block the outlet when the valve is in closed position, a pressure spring pressing the gate disc against the seat face when the valve is in closed position, and a ball transferring the reaction of the spring to the body. The closure further includes a stem extending into a port through the body, a plate engaging the tip of the stem, a helical spring engaging the plate, and a screw cap encompassing the length of the spring and engaging a threaded cuff extending from the body. The cap bears on the spring at its end opposite from that which engages the plate, the helical spring urging the valve closure to a closed position in which a shoulder on the closure engages the seat ring, providing a travel limit stop, and retaining the closure in the body. An outlet part secured to the body over the outlet retains the seat ring in the body.
The valve described in U.S. Pat. No. 4,456,028 is not suitable for use in the subsea environment. It requires manual adjustment for setting the opening pressure and does not compensate for the hydrostatic pressure. Moreover, it has no means for preventing backflow through the valve if, for any reason, the outlet pressure exceeds the inlet pressure. The present invention solves these problems.